The solid oxide fuel cell (hereinafter, referred to as SOFC) is known as a high efficiency fuel cell with a wide range of uses. The operating temperature of the SOFC is increased to increase the ionic conductivity, so air discharged from the compressor of a gas turbine can be used as air (oxidizing agent) supplied to the air electrode side. Also, high-temperature fuel that could not be used in an SOFC can be used as the fuel in the combustor of a gas turbine.
Therefore, various combinations of an SOFC, a gas turbine, and a steam turbine have been proposed as power generation systems that can achieve high efficiency power generation, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2009-205930A. The combined system disclosed in Japanese Unexamined Patent Application Publication No. 2009-205930A includes an SOFC, a gas turbine combustor that burns exhaust fuel gas and exhaust air discharged from the SOFC, and a gas turbine having a compressor that compresses air for supply to the SOFC.